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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made December 15, 2017

 Days 3-7Days 8-14Probabilistic Days 8-14
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Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Monday December 18, 2017 to Friday December 29, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST December 15 2017

Synopsis: A cold front is forecast to move across the Great Lakes during the middle of next week. South of this front, a low-pressure system is forecast to spin-up over the Lower Mississippi Valley. Later in the week, a low-pressure system is forecast to move from the Pacific Northwest to the Great Plains and eventually the Great Lakes by next weekend, bringing active weather along that entire track. A stormy pattern is predicted for western and Southern Alaska.

Hazards Detailed Summary

For Monday December 18 - Friday December 22: Low pressure over southeastern Canada should support high winds from the Great Lakes to the Northeast. Winds over the Great Lakes could exceed 35 knots, before the threat shifts eastward, where winds over the mountains of the Northeast are likely to exceed 50 mph.

Over the Southeast, a low-pressure system is forecast to develop along a remnant front. Heavy rains (up to 2 inches in 24 hours) are likely during Dec 18-19, with a low threat of isolated severe weather. Model timing on the progression of the convection limits predictability at this time.

A low-pressure system moving into the Pacific Northwest is likely to spread heavy precipitation at lower elevation with heavy snow at higher elevation and further inland, Dec 18-19. This system is forecast to move across the Northern Rockies and reintensify over the Great Plains. Warm advection snows are likely over the Great Lakes region later next week.

A period of high winds over Southern California is likely later next week. Models are showing wind speeds of at least 30 mph, which implies even higher values in the locations where terrain funneling can increase wind speeds.

An active pattern is forecast for southern Alaska, with high winds (in excess of 45 mph) for the Alaska Peninsula and the Aleutians, and high significant wave heights (exceeding 20 feet) surrounding the Aleutians Dec 18-19. Another potential period of high significant wave heights is forecast on Dec 20-21, but uncertainty is too high to depict a hazard at this time. Interior Alaska is likely to experience temperatures much above normal, for an extended period of time. Another low-pressure system is forecast to move northward from the Gulf of Alaska, and bring heavy precipitation (2 inches of liquid equivalent in 12 hours) to parts of Alaska on Dec 22. Model forecasts are uncertain about the specific location (Kenai Peninsula to Northern Panhandle), but both the GFS and ECMWF models show a potential for a storm system.

For Saturday December 23 - Friday December 29: Week-2 is likely to feature a continuation of the warmth over Alaska, though muted compared to the recent days. There is at least a 20 percent chance of maximum temperatures being above the 85th percentile during the early portion of period, with only a couple of days exceeding a 40 percent chance of exceeding the 85th percentile.

Over the CONUS, a slight risk (20-40 percent chance) of much below normal minimum temperatures is forecast from the Rockies to the Gulf Coast and northward to the Great Lakes and Northeast (Dec 24-29). Within that slight risk area, an area of a moderate risk (40-60 percent chance) of much below normal minimum temperatures is indicated over the Southern Plains (Dec 25-26), and another area over the Great Lakes (Dec 25-27).

Models continue to indicate the threat for heavy precipitation over the Tennessee Valley during the early portions of Week-2. Today, with some more specificity, models are also indicating the potential for low-level cold air to interact with the precipitation, leading to the introduction of a frozen precipitation hazard over the Tennessee Valley and Southern Appalachians. Additionally, the pattern is likely to support multiple events with orographically enhanced precipitation from Montana to eastern Colorado. Later in Week-2, days 10-12, most models indicate a translation of the storm activity from the Lower Mississippi Valley to the Northeast, though the impacts and timing are too uncertain to depict a hazard at this time.

The U.S. Drought Monitor, updated on Dec 12, shows an increase in areas of exceptional drought (D2-D4) to 6.49% from 5.99%. Most of the newly indicated severe drought was over the Southern Plains.

Forecaster: Matthew Rosencrans

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Click here to see a display of the GFS Ensemble Forecasts

Please consult local NWS Forecast Offices for short range forecasts and region-specific information.